1. Field of the Invention
The present invention relates to an electrophotographic toner and a developer comprising the same. The invention also relates to a fixing process and a fuser unit for fixing a toner image made with said toner, and an image-forming apparatus using said toner.
2. Description of the Related Art
In electrophotographic image-forming processes, generally, an electrophotographic image is formed by the steps of forming an electrostatic latent image on a photoreceptor drum by use of photoelectric effects, developing the latent image with toners into a toner image (a visible image), transferring and fixing the toner image onto a recording paper.
The fixation is performed by a fuser unit using heat, pressure, light or the like. One of the most commonly-used fuser units uses a heated roller.
Although a fuser unit using a heated roller has a high heat efficiency, the heated roller takes several tens of seconds for the initial heating (starting-up), and it is likely that residual toners on the roller are offset transferred onto a recording paper. In addition, since the roller nips a recording paper, papers fed continuously are likely to wrinkle or break by snaking their way.
A pressure fuser unit draws attention, since it has no use for warming-up and a heat source. However, it has difficulty in firmly fixing a toner image on a recording paper. In addition, since pressure is applied to a recording paper between a pair of rollers, the paper is likely to wrinkle or tear by snaking its way. Furthermore, in the case of using as a recording paper a stick-on label, which is frequently used in these days, the adhesive can be pressed out.
A light fuser unit can fix a toner image rapidly, since the toners forming the toner image are fused by absorbing selectively the energy of flash light from the light source, such as a xenon lamp, of the unit. Since such a fuser unit does not need to contact a recording paper, a toner image on the paper can be fixed without offset transferring toners onto the paper, wrinkling or tearing the paper resulting from snaking, or pressing out the adhesive in case of using a stick-on label.
In flash light fixing, black toners absorb light of all wavelengths and thus can be fused sufficiently and fixed firmly by absorbing strong near-infrared light in a range of 800 to 1000 nm from a xenon lamp, but color toners such as cyan, magenta and yellow toners hardly absorb such near-infrared light and therefore are fused insufficiently.
In this view, Japanese Kokai (laid-open) Patent Publication No. Hei 11-38667 (1999) proposes the addition of such an infrared-absorbent that absorbs near-infrared light to color toners.
However, infrared-absorbents having a strong absorption peak in the near-infrared region also absorb light of less than 780 nm in the visible region. Therefore, if toners contain a sufficient amount of such absorbents to be fused sufficiently by near-infrared light, toner images made with the toners are poor in color reproducibility due to absorption of light in the visible region.
In order to reduce the amount of infrared-absorbents to be added, Japanese Kokai (laid-open) Patent Publication No. 2008-107576 proposes a fixing process and a fuser unit with increased heat supply efficiency, in which flash light fixing is combined with laser light fixing wherein laser beams are specific for the used color toners respectively, that is, the wavelengths of the laser beams match the maximum absorption wavelengths of the respective color toners.
Japanese Kokai (laid-open) Patent Publication No. 2005-17442 describes that by limiting, to a given range of values, the viscoelasticity of toners containing infrared absorbents used for non-contact fixing (flash light fixing), a toner image made with the toners can be fixed with low energy and also white spots are prevented from occurring in the image.
The method described in the '576 publication does not significantly decrease the amount of infrared-absorbents added to toners and toner images made with such toners are poor in color reproducibility. In addition, since the fuser unit using said method requires a flash light unit and a laser light unit, it has a complex structure and thus is expensive to produce.
The '442 publication describes only the necessary viscoelasticity of toners containing infrared-absorbents for preventing white spots from occurring in a non-contact (flash light) fixed toner image. It does not describe about how to prevent white spots from occurring in a non-contact fixed toner image that is made with toners not containing an infrared-absorbent, which behave under light irradiation differently from toners containing an infrared-absorbents.